It is well known that microorganisms and suspended solids in potable water vary widely in composition depending on the source, and form microbial growth and sedimentation on the surfaces of piping and reservoirs wherever the water is contained. It is also well known that the sedimentation and the accumulation of microbial growth in still water promote the proliferation of various bacteria and cause the contamination of the water.
Plumbing regulations and plumbing codes are very explicit about preventing cross connections in a piping system and generally, licensed plumbers are apprehensive of these problems. A ‘cross connection’ is defined in plumbing code books as any actual or potential connection between a potable water system and any source of pollution or contamination.
The water quality leaving a municipal treatment plant is evaluated in terms of acceptable coliform count or acceptable e. coli count per unit of volume. These acceptable concentrations are considered harmless in drinking water. However, the water does not flow at a constant speed in a water distribution system, and what is considered an acceptable concentration diluted in the source end of a large water main may be less acceptable down the line as the water movement decreases. It is believed that the bacterial count due to accumulation and proliferation of micro-organisms could increase beyond the acceptable level in the extremities of a piping system.
It is generally well accepted that stagnant water should always be considered contaminated and non-potable. Further, it is believed that stagnant water is not only found in marshes and ponds, but is also found in water distribution piping systems and reservoirs that do not have sufficient flow to keep the water active, where water remains still for long period of time for example. Although the fact is often neglected, decaying water in a piping system is in direct contact with potable water and represents a cross-connection contamination that is believed to be harmful to the health of users supplied in water by that piping system.
Generally, municipal water distribution systems are flushed periodically to discharge stagnant water. It is often the case that the discharged water has a foul odour and filthy discolouration. Despite these periodic flushes, it is believed that the stagnation of water in municipal piping systems is a major cause of bad water taste, buildup of sediments in residential hot water reservoirs, and microbial growth in toilet reservoirs and in the drains of bathroom accessories. It is further believed that stagnant water in a piping system is a source of many persistent illnesses, digestive problems and the beginning of many diseases to those using and drinking water from these systems.
Another reason for periodically flushing water distribution systems is to eliminate concentrations of chlorine or other disinfectant used in water supply systems which tend to accumulate at regions of low flow or of stagnation. In addition to being detrimental to a good health, high concentrations of chlorine in particular, are known to change the PH value of the water and to deteriorate the protective coating inside water pipes. The material of fabrication of the pipes, which may contain traces of toxin substances are then exposed to the potable water.
The problem of water stagnation is particularly noticeable near water hydrants for example and at the ends of long branches of a piping system where the number of users on a branch pipe is not sufficient for ensuring a proper circulation of water. These situations are often found in newer or partly built subdivisions, and at the end of streets which are supplied in water by oversized pipes. Furthermore, a number of municipalities have water supply systems that were designed according to fire fighting requirements. The size of many branch pipes in these systems is often too large to ensure an adequate circulation of water within the pipe under normal conditions.
The problem of stagnant water in potable water distribution systems has been partly addressed in the past, as can be appreciated from the following prior art documents:    U.S. Pat. No. 2,445,414 issued on Jul. 20, 1948 to W. F. Zabriskie et al. This document discloses a partitioned riser pipe leading to a hydrant, in which water is circulated upward in one side of the pipe and down in the other side. The partitioned pipe is used to circulate water in the casing of the hydrant to prevent freezing of the water inside the hydrant head.    U.S. Pat. No. 3,481,365 issued on Dec. 2, 1969 to A. R. Keen. This patent discloses various partitions in a piping system to divert the water flow near the branch valves in that piping system. The partitions are used to prevent stagnation of water near the branch valves.    U.S. Pat. No. 5,476,118 issued on Dec. 19, 1995 to Ikuo Yokoyama. This document discloses the use of a venturi eductor and venturi tube in an active water pipe to draw water from a valve body in a branch pipe connected to this water pipe, to prevent stagnation of water in the valve body.    U.S. Pat. No. 6,062,259 issued on May 16, 2000 to Blair J. Poirier; the applicant of the present patent application. This document describes a system for recirculating water in the branches of a municipal water distribution system. The main feature of this invention consists of a pumping system having means to draw water from the far end of a branch pipe relative to the water main and to convey this water into the near end of the branch pipe to circulate the water in the branch pipe.    CA 2,193,494 issued on Dec. 7, 1999 to Perry et al. This document discloses a method of cleaning and maintaining potable water distribution pipe system with a heated cleaning solution. The heated cleaning solution is circulated in the piping system to dislodge and flush all accumulated contaminants.
Although substantial efforts have been made in the past to propose solutions to prevent the stagnation of water in piping systems, these proposals continue to be treated with uncertainty by water system designers. For this reason basically, it is believed that there continues to be a need for a better solution which is more practicable than the prior art proposals.